Kaikohe, Kerikeri, to Whangarei. Activity began about 9 Ma, and the youngest cones are probably only tens of thousands of years old. Little Barrier Island is the emergent part of a large dacitic-rhyodacitic stratovolcano, formed through two eruptive periods (3 Ma, and 1.6–1.2 Ma). Coastal dunes The coastal barriers north and south of the entry to the Kaipara Harbour, are essentially consolidated sand dunes, built up over the last few million years. Similar dunes have formed in the north from Ahipara to Cape Reinga, connecting what used to be isolated islands to the rest of the North Island, thus creating a large tombolo. Sand on the eastern coast tends to be more pure quartz, and appears white. Geothermal areas Hot springs exist at Ngawha Springs, with temperatures around 40–50 °C. There are also hot springs at Waiwera and Parakai, in the southern part of the Northland Peninsula, in the Auckland Region. All are used for hot pools. The Ngawha geothermal field is also used for the generation of electricity. Geological resources Copper has been mined at Kaeo, silver, gold and mercury at Puhipuhi, and antimony at Russell. Coal has been mined at Kawakawa, Hikurangi, Kamo and Kiripaka. The Northland Basin, to the west of the Northland Peninsula is considered as having potential for oil and gas. Halloysite clay is mined at Matauri Bay and Mahimahi. High quality quartz sand is dredged from near Parengarenga Harbour. Geological hazards The main geological hazard in Northland is the potential for landslides, particularly in mudstones and sandstones of the Northland Allochthon. Northland has the least incidence of earthquakes of anywhere in New Zealand. However, tsunamis generated by earthquakes around the Pacific can occur on the east coast. Geological sites of interest Hunua Terrane can be seen along much of the coast between the Bay of Islands and Whangarei. Mount Camel Terrane can be seen at Parerake Bay, Karikari Peninsula. Kamo coal measures can be seen near Kamo. Whangarei Limestone can be seen at Waro Rocks Scenic Reserve, north of Hikurangi. Many of the hills in Northland are formed from the Tangihua Complex rocks of the Northland Allochthon. Maungaraho, north of Tokatoka, gives a good example of a remnant of an early Miocene andesitic volcano. Whangarei Heads represents another example. Sand dunes can be seen on either side of the coast between Kaitaia and Cape Reinga. Maps Geological maps of New Zealand can be obtained